U.S. Pat. Nos. 5,003,865 and 5,131,887 to Traudt, titled "Pressure Controlled Fresh Air Supply Ventilation System Using Soil Gas Pressure As A Reference, And Method Of Use" describe a particularly relevant, although non-limiting, application for the present invention system. Said 865 and 887 Patents are incorporated by reference herein as they provide insight to the utility provided by the present invention system in a ventilation system for air pressure control in an enclosed space. As general interest, it is noted that the 865 and 887 Patents describe a ventilation system which utilizes soil gas pressure below an enclosed space as a reference pressure, to which enclosed space inside air pressure is compared by the system, during operation. The inlet supply air into the enclosed space is controlled by a device based upon an initial user set value, which set level of supply air, under normal conditions, then adjusted by ventilation system action to counteract changes in a signal derived by comparison of said soil gas pressure and inside enclosed space air pressure, by a differential pressure detecting device. While the 865 and 887 Patents describe utility providing systems, it has become apparent that a more accurate, reliable and economical differential pressure detecting device would optimize their operation.
Additionally, said 865 and 887 Patents further disclose that the quality of air in enclosed spaces such as houses and other buildings is subject in an Environmental Protection Agency Report titled "EPA Report to Congress on Indoor Air Quality", released Aug. 4, 1989. In that report reference is made to the so called "Sick Building Syndrome" and a program of increased research and information dissemination regarding the dangers of poor indoor air quality is recommended. Health effects attributed to air contaminants accumulating in poorly ventilated houses and other buildings range from eye, ear, nose and throat irritation, to full scale respiratory and neurological diseases, genetic mutations and cancer. Contaminants such as radon, asbestos, tobacco smoke, formaldehyde, volatile organic compounds, chlorinated solvents, biological contaminants and pesticides etc., and the synergistic effects of multiple contaminants are cited as causes of health problems. The report suggests that reducing the sources of contaminants is the most direct and dependable option in overcoming the problem, and that while air cleaning equipment can compliment air quality improvement, there is no substitute for providing an adequate supply of fresh air into an enclosed space.
Further, said 865 and 887 Patents disclose that in recent years, the high cost of energy has led many people to strive to make their houses and buildings more tightly sealed, hence, in combination with the use of insulation, more energy efficient. Said efforts have included sealing cracks and other air leaks in their houses or buildings to prevent heated or cooled air from escaping, and outside air which requires heating or cooling, from randomly entering at an excessive rate. In effect, such houses and buildings become, to various degrees, closed systems. In such structures the fresh air supply rate is often reduced to far below the American Society of Heating, Refrigeration and Air Conditioning Engineers presently recommended fresh air inlet volume flow rate of 15 Cubic Feet per Minute (CFM) per inhabitant, or 35% air changes per hour, whichever is greater, (see ASHRAE Standard 62-1989). The result of an insufficient fresh air supply into, and stale air removal from such tight enclosed spaces is that contaminants accumulate inside same to dangerous health affecting levels. To emphasize this point, it is estimated by some health care researchers that presently two persons per hour, in the United States alone, contract lung cancer as a result of contact with radon in poorly ventilated houses and other buildings.
A search of existing Patents during preparation of the 865 and 887 Patents showed that numerous inventors have proposed systems, and methods of their use, which provide controlled ventilation to enclosed spaces such as houses and buildings. The various approaches basically utilize a means to cause air flow, such as a motor driven blower, to cause air to move into and stale air to move out of an enclosed space. The fresh air volume supply rate is typically, but not necessarily in the most basic schemes, controlled based upon signals developed by sensing air pressure differences between the inside and the outside of a house or building, from signals derived from sensed rates of air flows in various parts of a system, or by sensing the velocity of the wind outside the house or building.
The most basic schemes simply provide a large fresh air supply into a house or building sufficient to raise the air pressure inside the house or building to a large positive value with respect to that outside the house or building. In such a scheme the fresh air supply must be large enough to maintain the large positive pressure difference no matter what active or passive exhaust air flows develop. As an example, operating a clothes dryer or fireplace will actively exhaust air from a house, and opening a door to the outside of the house or building can passively increase exhaust air. The problem with such simple large excessive positive pressure systems is that they are wasteful of energy. The large volume of fresh air which flows into a house or building equipped with such a system must be heated or cooled at times. As a very large fresh air supply rate is not necessary to keep contaminant concentration levels low enough for health maintenance reasons, there is no valid reason to provide it to a tight house or building.
It should now be obvious that ventilation in buildings and houses etc. should be carefully controlled so that an adequate oxygen supply is assured, contaminants in the air are filtered out, and excess air leakage into and out of enclosed spaces is minimized. To do so, however, requires a precise means for monitoring pressure differences between the enclosed space and a reference pressure such as outdoor air pressure or soil gas pressure. The present invention differential pressure detecting system precisely monitors the pressure difference between first and second environments.
While the said 865 and 887 Patents provided a ventilation control system which identifies and utilizes a pressure reference, (which is compared to air pressure in an enclosed space controlled environment), so a signal can be derived and variation in the signal can be used to control the fresh air supply rate into, and stale air exhaust rate out of an enclosed space controlled environment, a need remains for a reliable and economical differential pressure detecting system for monitoring very small pressure differentials between first and second environments. A Search of Patents for systems somehow relevant to that of the present invention has identified a Sullivan, U.S. Pat. No. 4,031,847 which describes an improvement for responding to reversal in the sense of the ratio between two pressures. In a housing there is located a generally cup-shaped indicator element of resilient, air inpenetratable material including a slack diaphragm having a central area of augmented visibility and an integral tongue projecting obliquely therefrom. The diaphragm is self-biased in either of two positions, in one of which the tongue conceals the central area, and in the other of which the tongue exposes the central area. Pressures to be compared are applied on opposite sides of the diaphragm, with said diaphragm being observable through an observation window. Patents which describe capacitance based transducer systems are U.S. Pat. No. 4,370,890 to Frick; U.S. Pat. No. 5,271,277 to Pandorf; and U.S. Pat. No. 4,176,557 to Johnston. A Patent describing a piezoelectric pressure transducer is U.S. Pat. No. 5,088,329 to Sahagen. Patent to Onuma et al., U.S. Pat. No. 4,189,724 which describes a restriction indicator which comprises a contactless photo-inturrupter switch device including light emitting, and light receiving devices.
Also disclosed, as it is known, is a pressure transducer manufactured by the Henry G. Dietz Co., Model LPS 100. It is capable of activating gold coated contacts in the presence of 0.005 inches of mercury.
The present invention responds to a need for a more reliable and economical differential pressure detecting system than is known in the marketplace, for monitoring very small pressure differentials between first and second environments with a system which can be applied in essentially any setting wherein it is desired to accurately monitor a differential in pressure between first and second environments.